Although applicable in principle to any desired combination of dielectrics, the present invention and the problem area on which it is based are discussed with regard to silicon dioxide as the first dielectric and a transition metal oxide having a high k value (k=relative permittivity or dielectric constant) as the second dielectric.
So-called dielectrics having a high k value (also referred to as high-k materials) have been used for some time as capacitor dielectrics in semiconductor memory devices. These high-k materials are likewise used in MOSFETS as an alternative gate dielectric, to be precise in particular in 70 nm technology, since there direct tunneling and a pin-hole density no longer enable the use of silicon dioxide as the gate dielectric.
An overview of the current status of high-k materials is given by G. D. Wilk, R. M. Wallace, J. M. Anthony, “High-k gate electrics: Current status and materials properties considerations” in JOURNAL OF APPLIED PHYSICS, Vol. 89, No. 10, pages 5243–5275.
In particular, this article discloses using a first dielectric made of silicon dioxide with a silicon substrate and a second dielectric having a high k value made of a transition metal oxide above said first dielectric.
However, a disadvantage mentioned is that the minimum achievable equivalent thickness of such a two-layer dielectric will always be larger than the corresponding thickness of a single-layered dielectric made of silicon dioxide.